P2452Electrical fault in the particulate filter pressure sensor circuit

How the car works this out

The differential pressure sensor is a small unit mounted in the engine bay with two pipes running down to tapping points either side of the particulate filter. It reports the pressure difference as a voltage within a defined range. The control unit sets this code when that voltage sits at or beyond either electrical rail — as it would if the circuit were open, shorted to earth or shorted to a supply — or when the sensor draws current outside its expected window. It is an electrical judgement about the circuit rather than an assessment of whether the value makes sense.

What you might notice

• Engine management lamp, often with the particulate filter lamp as well
• Regenerations stopping entirely, with no long-drive prompt ever appearing
• Reduced power on cars that respond by limiting the engine
• Over the following weeks, symptoms of a genuinely loading filter that were not there when the code first appeared

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1. 1A corroded connector or water ingress at the sensor plugCommon

   How to check: Unplug and inspect the pins. Green corrosion or moisture in the plug is common and is a far cheaper fix than a sensor.

2. 2Chafed, broken or heat-damaged wiring between the sensor and the control unitCommon

   How to check: Wiggle the loom near the sensor while the live reading is displayed. A value that jumps around as you move it is a wiring fault.

3. 3A failed sensorCommon
4. 4A fault in the shared five-volt supply or earth serving several sensors, which typically shows up as multiple sensor codes at oncePossible

   How to check: Read all the stored codes. Several unrelated sensors reporting circuit faults simultaneously points at the shared supply rather than at any one of them.

5. 5Damage to the sensor or its loom during previous exhaust or turbocharger workPossible
6. 6A failed input circuit in the control unitLess common

What to do about it

1. 1Deal with this one sooner than its apparent seriousness suggests. Most control units suspend particulate filter regeneration when they have no valid pressure signal, so every mile driven with the code stored adds soot to a filter that is no longer being cleaned.
2. 2Check the connector and the wiring before buying a sensor. Corrosion and chafing are at least as likely as the sensor itself, and both are cheaper.
3. 3Read every code stored, not just this one. Several sensors reporting circuit faults at once means a shared supply or earth problem rather than several coincidental failures.
4. 4After the repair, expect the car to want a regeneration fairly promptly, and give it the sustained drive it asks for rather than switching off part way through.
5. 5If the car has covered a lot of miles with this code stored, mention that to the garage so they can assess the filter's actual soot load rather than assuming it starts from where it left off.

Will it fail an MOT?

The lamp is a major defect on diesels first used on or after 1 July 2008, and that fails the car on its own. The more interesting MOT risk with this code is the one that builds up while it is ignored. Because regeneration is usually suspended without a valid pressure reading, a car left with this fault arrives at its test with a filter genuinely loaded with soot, and a diesel fitted with a particulate filter fails if the exhaust emits visible smoke of any colour, as well as being measured against a smoke opacity limit during the metered acceleration test. In other words a car that would have failed on the lamp alone in month one can be failing on smoke as well by month six. There is a strong argument for fixing this promptly on cost grounds alone.